/*
 * Copyright 2013-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package com.cyx.netty.gateway.support;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * A class that performs some subnet calculations given a network address and a subnet mask.
 * See original from commons-net org.apache.commons.net.util.SubnetUtils
 * @see "http://www.faqs.org/rfcs/rfc1519.html"
 */
@SuppressWarnings("unused")
public class SubnetUtils {

	private static final String IP_ADDRESS = "(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})";
	private static final String SLASH_FORMAT = IP_ADDRESS + "/(\\d{1,3})";
	private static final Pattern addressPattern = Pattern.compile(IP_ADDRESS);
	private static final Pattern cidrPattern = Pattern.compile(SLASH_FORMAT);
	private static final int NBITS = 32;

	private int netmask = 0;
	private int address = 0;
	private int network = 0;
	private int broadcast = 0;

	/** Whether the broadcast/network address are included in host count */
	private boolean inclusiveHostCount = false;


	/**
	 * Constructor that takes a CIDR-notation string, e.g. "192.168.0.1/16"
	 * @param cidrNotation A CIDR-notation string, e.g. "192.168.0.1/16"
	 * @throws IllegalArgumentException if the parameter is invalid,
	 * i.e. does not match n.n.n.n/m where n=1-3 decimal digits, m = 1-3 decimal digits in range 1-32
	 */
	public SubnetUtils(String cidrNotation) {
		calculate(cidrNotation);
	}

	/**
	 * Constructor that takes a dotted decimal address and a dotted decimal mask.
	 * @param address An IP address, e.g. "192.168.0.1"
	 * @param mask A dotted decimal netmask e.g. "255.255.0.0"
	 * @throws IllegalArgumentException if the address or mask is invalid,
	 * i.e. does not match n.n.n.n where n=1-3 decimal digits and the mask is not all zeros
	 */
	public SubnetUtils(String address, String mask) {
		calculate(toCidrNotation(address, mask));
	}


	/**
	 * Returns <code>true</code> if the return value of {@link SubnetInfo#getAddressCount()}
	 * includes the network and broadcast addresses.
	 * @since 2.2
	 * @return true if the hostcount includes the network and broadcast addresses
	 */
	public boolean isInclusiveHostCount() {
		return inclusiveHostCount;
	}

	/**
	 * Set to <code>true</code> if you want the return value of {@link SubnetInfo#getAddressCount()}
	 * to include the network and broadcast addresses.
	 * @param inclusiveHostCount true if network and broadcast addresses are to be included
	 * @since 2.2
	 */
	public void setInclusiveHostCount(boolean inclusiveHostCount) {
		this.inclusiveHostCount = inclusiveHostCount;
	}



	/**
	 * Convenience container for subnet summary information.
	 *
	 */
	public final class SubnetInfo {
		/* Mask to convert unsigned int to a long (i.e. keep 32 bits) */
		private static final long UNSIGNED_INT_MASK = 0x0FFFFFFFFL;

		private SubnetInfo() {}

		private int netmask()       { return netmask; }
		private int network()       { return network; }
		private int address()       { return address; }
		private int broadcast()     { return broadcast; }

		// long versions of the values (as unsigned int) which are more suitable for range checking
		private long networkLong()  { return network &  UNSIGNED_INT_MASK; }
		private long broadcastLong(){ return broadcast &  UNSIGNED_INT_MASK; }

		private int low() {
			return (isInclusiveHostCount() ? network() :
					broadcastLong() - networkLong() > 1 ? network() + 1 : 0);
		}

		private int high() {
			return (isInclusiveHostCount() ? broadcast() :
					broadcastLong() - networkLong() > 1 ? broadcast() -1  : 0);
		}

		/**
		 * Returns true if the parameter <code>address</code> is in the
		 * range of usable endpoint addresses for this subnet. This excludes the
		 * network and broadcast adresses.
		 * @param address A dot-delimited IPv4 address, e.g. "192.168.0.1"
		 * @return True if in range, false otherwise
		 */
		public boolean isInRange(String address) {
			return isInRange(toInteger(address));
		}

		/**
		 *
		 * @param address the address to check
		 * @return true if it is in range
		 * @since 3.4 (made public)
		 */
		public boolean isInRange(int address) {
			long addLong = address & UNSIGNED_INT_MASK;
			long lowLong = low() & UNSIGNED_INT_MASK;
			long highLong = high() & UNSIGNED_INT_MASK;
			return addLong >= lowLong && addLong <= highLong;
		}

		public String getBroadcastAddress() {
			return format(toArray(broadcast()));
		}

		public String getNetworkAddress() {
			return format(toArray(network()));
		}

		public String getNetmask() {
			return format(toArray(netmask()));
		}

		public String getAddress() {
			return format(toArray(address()));
		}

		/**
		 * Return the low address as a dotted IP address.
		 * Will be zero for CIDR/31 and CIDR/32 if the inclusive flag is false.
		 *
		 * @return the IP address in dotted format, may be "0.0.0.0" if there is no valid address
		 */
		public String getLowAddress() {
			return format(toArray(low()));
		}

		/**
		 * Return the high address as a dotted IP address.
		 * Will be zero for CIDR/31 and CIDR/32 if the inclusive flag is false.
		 *
		 * @return the IP address in dotted format, may be "0.0.0.0" if there is no valid address
		 */
		public String getHighAddress() {
			return format(toArray(high()));
		}

		/**
		 * Get the count of available addresses.
		 * Will be zero for CIDR/31 and CIDR/32 if the inclusive flag is false.
		 * @return the count of addresses, may be zero.
		 * @throws RuntimeException if the correct count is greater than {@code Integer.MAX_VALUE}
		 * @deprecated (3.4) use {@link #getAddressCountLong()} instead
		 */
		@Deprecated
		public int getAddressCount() {
			long countLong = getAddressCountLong();
			if (countLong > Integer.MAX_VALUE) {
				throw new RuntimeException("Count is larger than an integer: " + countLong);
			}
			// N.B. cannot be negative
			return (int)countLong;
		}

		/**
		 * Get the count of available addresses.
		 * Will be zero for CIDR/31 and CIDR/32 if the inclusive flag is false.
		 * @return the count of addresses, may be zero.
		 * @since 3.4
		 */
		public long getAddressCountLong() {
			long b = broadcastLong();
			long n = networkLong();
			long count = b - n + (isInclusiveHostCount() ? 1 : -1);
			return count < 0 ? 0 : count;
		}

		public int asInteger(String address) {
			return toInteger(address);
		}

		public String getCidrSignature() {
			return toCidrNotation(
					format(toArray(address())),
					format(toArray(netmask()))
			);
		}

		public String[] getAllAddresses() {
			int ct = getAddressCount();
			String[] addresses = new String[ct];
			if (ct == 0) {
				return addresses;
			}
			for (int add = low(), j=0; add <= high(); ++add, ++j) {
				addresses[j] = format(toArray(add));
			}
			return addresses;
		}

		/**
		 * {@inheritDoc}
		 * @since 2.2
		 */
		@Override
		public String toString() {
			final StringBuilder buf = new StringBuilder();
			buf.append("CIDR Signature:\t[").append(getCidrSignature()).append("]")
					.append(" Netmask: [").append(getNetmask()).append("]\n")
					.append("Network:\t[").append(getNetworkAddress()).append("]\n")
					.append("Broadcast:\t[").append(getBroadcastAddress()).append("]\n")
					.append("First Address:\t[").append(getLowAddress()).append("]\n")
					.append("Last Address:\t[").append(getHighAddress()).append("]\n")
					.append("# Addresses:\t[").append(getAddressCount()).append("]\n");
			return buf.toString();
		}
	}

	/**
	 * Return a {@link SubnetInfo} instance that contains subnet-specific statistics
	 * @return new instance
	 */
	public final SubnetInfo getInfo() { return new SubnetInfo(); }

	/*
	 * Initialize the internal fields from the supplied CIDR mask
	 */
	private void calculate(String mask) {
		Matcher matcher = cidrPattern.matcher(mask);

		if (matcher.matches()) {
			address = matchAddress(matcher);

            /* Create a binary netmask from the number of bits specification /x */
			int cidrPart = rangeCheck(Integer.parseInt(matcher.group(5)), 0, NBITS);
			for (int j = 0; j < cidrPart; ++j) {
				netmask |= (1 << 31 - j);
			}

            /* Calculate base network address */
			network = (address & netmask);

            /* Calculate broadcast address */
			broadcast = network | ~(netmask);
		} else {
			throw new IllegalArgumentException("Could not parse [" + mask + "]");
		}
	}

	/*
	 * Convert a dotted decimal format address to a packed integer format
	 */
	private int toInteger(String address) {
		Matcher matcher = addressPattern.matcher(address);
		if (matcher.matches()) {
			return matchAddress(matcher);
		} else {
			throw new IllegalArgumentException("Could not parse [" + address + "]");
		}
	}

	/*
	 * Convenience method to extract the components of a dotted decimal address and
	 * pack into an integer using a regex match
	 */
	private int matchAddress(Matcher matcher) {
		int addr = 0;
		for (int i = 1; i <= 4; ++i) {
			int n = (rangeCheck(Integer.parseInt(matcher.group(i)), 0, 255));
			addr |= ((n & 0xff) << 8*(4-i));
		}
		return addr;
	}

	/*
	 * Convert a packed integer address into a 4-element array
	 */
	private int[] toArray(int val) {
		int ret[] = new int[4];
		for (int j = 3; j >= 0; --j) {
			ret[j] |= ((val >>> 8*(3-j)) & (0xff));
		}
		return ret;
	}

	/*
	 * Convert a 4-element array into dotted decimal format
	 */
	private String format(int[] octets) {
		StringBuilder str = new StringBuilder();
		for (int i =0; i < octets.length; ++i){
			str.append(octets[i]);
			if (i != octets.length - 1) {
				str.append(".");
			}
		}
		return str.toString();
	}

	/*
	 * Convenience function to check integer boundaries.
	 * Checks if a value x is in the range [begin,end].
	 * Returns x if it is in range, throws an exception otherwise.
	 */
	private int rangeCheck(int value, int begin, int end) {
		if (value >= begin && value <= end) { // (begin,end]
			return value;
		}

		throw new IllegalArgumentException("Value [" + value + "] not in range ["+begin+","+end+"]");
	}

	/*
	 * Count the number of 1-bits in a 32-bit integer using a divide-and-conquer strategy
	 * see Hacker's Delight section 5.1
	 */
	int pop(int x) {
		x = x - ((x >>> 1) & 0x55555555);
		x = (x & 0x33333333) + ((x >>> 2) & 0x33333333);
		x = (x + (x >>> 4)) & 0x0F0F0F0F;
		x = x + (x >>> 8);
		x = x + (x >>> 16);
		return x & 0x0000003F;
	}

	/* Convert two dotted decimal addresses to a single xxx.xxx.xxx.xxx/yy format
	 * by counting the 1-bit population in the mask address. (It may be better to count
	 * NBITS-#trailing zeroes for this case)
	 */
	private String toCidrNotation(String addr, String mask) {
		return addr + "/" + pop(toInteger(mask));
	}
}
